Method and apparatus for increasing the efficiency of corona charging of a photoconductor

ABSTRACT

A method and apparatus for increasing the efficiency of corona charging of a photoconductive plate are disclosed in the present application. The method comprises reducing the electromagnetic radiation received by the photoconductive plate by the use of an optical mask between the charging corona wires and the photoconductive plate. In one embodiment, the ions produced by the corona wire are directed to the photoconductive plate by the use of a combination of electrostatic ion deflection techniques and/or the use of a gas flow to carry the ions around an optical mask. In another embodiment, the efficiency of corona charging is increased by charging an intermediate insulating material such as insulating beads or an insulating belt which may then be brought into contact with an optically shielded photoconductor or other material to be charged.

United States Patent Walter Roth Rochester;

Charles F. Gallo, Penfield; Algrid G. Leiga, Pittsford; John A. Mclnally, Penfield, N.Y. 665,049

Sept. 1, 1967 Jan. 19, 197 1 Xerox Corporation Rochester, N.Y.

a corporation oi New York Inventors Appl. No. Filed Patented Assignee METHOD AND APPARATUS FOR INCREASING THE EFFICIENCY OF CORONA CHARGING OF A PHOTOCONDUCTOR 6 Claims, 5 Drawing Figs.

US. Cl 250/49.5, 317/262 Int. Cl G03g 13/92, 603g 15/02 Field ofSearch ..117/17.5;-

[56] References Cited UNITED STATES PATENTS 2,863,063 12/1958 Schulze 250/49.5X 2,934,650 4/1960 De Witt 250/49.5 3,084,061 4/1963 Hall 1 17/175 3,409,768 11/1968 Whitmore et al. 250/49.5

Primary Examiner-William F. Lindquist Att0rneysRonald Zibelli and Norman E. Schrader & James J. Ralabate ABSTRACT: A method and apparatus for increasing the efficiency of corona charging of a photoconductive plate are disclosed in the present application. The method comprises reducing the electromagnetic radiation received by the photoconductive plate by the use of an optical mask between the charging corona wires and the photoconductive plate In one embodiment, the ions produced by the corona wire are directed to the photoconductive plate by the use of a combination of electrostatic ion deflection techniques and/or the use of a gas flow to carry the ions around an optical mask.

in another embodiment, the efficiency of corona charging is increased by charging an intermediate insulating material such as insulating beads or an insulating belt which may then be brought into contact with an optically shielded photoconductor or other material to be charged.

PATENTEM sum 1 or 2 3.557.367

DC 12 //POWER 22 SUPPLY a BIAS MATR|X l6 l8 20 19 FIG. 2

BIAS MATRIX INVENTORS WALTER ROTH CHARLES F. GALLO ALGRID c. LEIGA FIG. 3 BYzIOHN A: M CENAZ Y A TTORNEVS PATENTEU JAN] 91911 3557367 sum 2 0r 2 5 INVENTORS WALTER ROTH CHARLES F. GALLO AL RID G G. LEIGA BiJOHN A. MC NALLY A TTORNEYS METHOD AND APPARATUS FORINCREASING THE EFFICIENCY OF CORONA CHARGING OF A PIIOTOCONDUCTOR BACKGROUND OF THE INVENTION In general the present invention relates to corona charging and more specifically to a method and apparatus for increasing the efficiency of corona charging. Corona charging has become almost universally used as a method of sensitizing xerographic photoreceptors. A large flux of ions is created by the corona discharge of a wire or wire array which is maintained at a high potential and supported near the photoconductor. These ions produced by the corona wire result in a deposition of charge'on the photoconductor or photoreceptor and sensitize its surface for later exposure or the like in the xerographic process. In addition to producing-ion for the charging process, the corona also generates electromagnetic radiation which can be observed visually. Although its intensity of the electromagnetic radiation from the corona appears weak to the human eye, the main emission is in the ultraviolet portion of the spectrum which is outside of the eye response. Since the sensitivity of xerographic selenium plates is relatively high in the ultraviolet region of the spectrum even ap-' parently weak radiation from the corona has a tendency to discharge the plate. It has been discovered that the electromagnetic radiation from charging coronas is not insignificant and that the radiation can be sufficiently intense to reduce the efficiency of the corona charging operation. As a result of electromagnetic radiation discharge, the charging efficiency with positive corona is adversely affected by approximately percent and may well be in excess of IO percent for specific photoreceptor combinations more sensitive than the selenium. The electromagnetic radiation from a negative corona is approximately five times more intense than the radiation from position corona under similar conditions. As a result the adverse affect of electromagnetic radiation from negative corona on equally sensitive photocoriductors may be expected to, in general, ex ceed that of the positive corona. Furthermore the discharge problem resulting from corona radiation becomes more severe as more sensitive photoconductors are developed for use in higher speed operational configurations.

The prior art methods and devices for corona charging produce less than the desired efficiency in corona charging and considerable difficulty is encountered as the photoreceptors being charged become more sensitive. This difficulty arises from the fact that the electromagnetic radiation produced by the charging corona serves to decrease the charging efficiency of that corona, a fact the significance of which has not been fully recognized or appreciated heretofore.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a corona charging which will result in an increased efficiency for high speed, sensitive photoconductors.

Other objects and a further understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings.

The present invention overcomes the deficiencies of the .prior art and achieves its objectives by providing an optical mask in the path of the electromagnetic radiation produced by the corona wire. The ions produced by the corona charging are guided around the optical mask by a combination of ion I deflection techniques and/or a supplementary gas flow, or by charging an intermediate material such as a large number of small insulating beads or an insulatingbelt. The intermediate material may then be cascaded or otherwise brought into contact with the photoconductor to achieve a charge transfer to the photoconductor.

BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate the understanding of this invention, reference will now be made to the appended drawings of the preferred embodiments of the present invention. The drawings should not be construed as limiting the invention but are exemplary only. In the drawings:

FlG.l is a front view of a corona charging device according to the present invention. including a partial cross section of the photoconductive drum.

FIG. 2 is a cross-sectional representation of the present invention taken along line 22 of FIG. l.

FIG. 3 is a cross-sectional representation of an alternative embodiment of the present invention.

FIG. 4 is a cross-sectional representation of another embodiment of the present invention.

FIG. 5 is a cross-sectional representation of yet another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention is shown in FIG. I in which corona charging unit 10 is positioned over and in close proximity to photoconductive drum 15 including a photoconductor 12 which overlays a grounded (2l) conductive backing l4. The corona charging device l0 comprises a corona wire I6 enclosed by a shield 18. At the orifice of the shield 18 is provided an electrostatic ion deflection element 20. A- suitably high potential from DC power supply 22 is applied to the electrostatic ion deflection element 20 and is of the same relative polarity as the ions produced by corona wire l6. A difference of potential suitable for producing the desired electrostatic ion deflection based upon the geometric configuration of the shield l8 and the ion deflection element 20 is provided, as illustrated, by a bias matrix 27 including, for example, an array of resistors 23, 24, 25, and 29 to provide a suitable potential difference between the electrostatic ion deflection element 20 and the corona wire 16. The specific circuitry employed may, of course, as would be obvious to one of .ordinary skill in the art, involve many other circuit elements other than the resistors 23, 24, 25 and 29 which are representative of a suitable electrical circuit for producing the desired electrical potentials between corona wire l6 and a shield 18 and an electrostatic ion deflection element 20. It should be noticed that the electrostatic shield 18 may also be biased so as to repel additional ions through the orifice in electrostatic deflection shields l8.

By applying proper potential differences by means well known in the art of ion optics suitable potentials may be applied through the backing plate l4, the electrostatic ion deflection element 20, the shield l8, and corona wire l6 to cause a flow of ions to pass around electrostatic ion deflection element 20 and be directed to the photoconductive or photoreceptor layer l2. It should be noted that because of its con figuration and relative dimensions to the photoreceptor l2 and the corona charging unit 10, electrostatic ion deflection element 20 prevents any electromagnetic radiation, which travels in a straight line, from reaching the photoconductor directly.

While a specific configuration of electrostatic ion deflection element 20 is illustrated in FIG. 2 any suitable configuration for a specific dimension and configuration of the rest of the system which will produce the desired electrostatic deflection of the ion beam while inhibiting or preventing the passage of any electromagnetic radiation to the photoreceptor l2 may be employed. The potentials applied may be altered both in polarity and in magnitude to provide the desired electrostatic deflection for the specific energies, configurations, and materials, being employed. Indeed, deflection element 20 need not be in the electrical circuit at all for some configurations and thus need not be a conductive metal but can be wood or other dielectric material. In the situation where the deflection element is a dielectric not in the circuit, element 20 merely builds up charges which serve to repel the ions produced by the corona discharge.

The structure and materials which make up the corona charging unit in this application may be of the type as taught in the numerous patents in this area, for example, 2,588,699, 2,777,957, 2,836,725. 2,885,556,;1nd 2,922,883.

In operation the ions produced by the corona wire l6 are radiated in all directions uniformly. The shield means l8 may be blackened with a conductive layer [9, such as colloidal graphite, platinum black, and the like so that large amounts of the normally reflected electromagnetic radiation will not be reflected so as to reach the photoconductor l2. In addition, direct radiation from corona wire I6 is masked by means of the electrostatic ion deflection element 20 which serves both to act as an optical mask and to provide a means for deflecting the ion current produced by corona wire l6 onward to the photoconductive surface 12.

An alternative configuration is illustrated in FIG. 3, in which in addition to the shielding means 18 and electrostatic deflection element 20, a flow of gas from compressed gas bottles 26 is provided. In FIG. 3 the gas flow is a dual flow having dual entrance ports 28 to shield [8. This flow of gas is produced by the pneumatic pressure of the compressed gas in bottles 26, and acts to carry the ion flow produced into the shield l8 in the area of corona wire l6 may beselected in one of several manners to ni minimize the problem of electromagnetic radiation as stated above for a v given set of conditions.

A gas may be selected with an optical spectrum outside the sensitivity range of the photoconductor. For example, oxygen or neon or a mixture of these gases may be utilized when a selenium plate is the material employed as photoconductor l2. It is also possible to utilize a gas whichabsorbs regions of the spectrum where the output radiation from the corona is high thus eliminating the electromagnetic radiation pattern to a large extent. It will be obvious to one having ordinary skillin the art that the gas flow may be utilized to direct the flow of ions around the optical mask element 20 by itself without any potential applied to optical mask element 20. In addition suitable potentials may be applied to the optical mask element 20 so that it continues to act as an electrostatic ion deflection element and in conjunction with the gas flow serves to direct the ions around itself as an optical mask and onto the photoconductive plate l2.

Thus, in summary of the operations involved in these em bodiments it may be said that optical mask means combined with a gas flow in a wide variety of configurations and with the gas itself having a wide variety of flow rates and effects upon the optical radiation may be utilized to result in effectively blocking the optical radiation produced by corona wire 16 from reaching the photoreceptive plate 12 and yet insure that an adequate supply of ions from corona wire 16 is directed to the surface to be charged 12.

Another embodiment of the present invention is shown in FIG. 4 which represents a charging system which utilizes small insulating beads 48 as the intermediate material. The'small insulating beads 48 are stored in a container 46 which feeds into the base of housing 52 for the corona unit 40. A motor 60 drives a belt 45 which contains a number of buckets 44 around a pair of pulley wheels 42 and 58. The configuration is such that the buckets 44 are caused to dip into the supply of small insulating beads 48 which lie in the base of unit 52. These beads are carried upward in buckets 44 and at the top of pulley wheel 42 are dumped onto support means 62. While sliding and rolling down support means 62 the beads 48 are charged by the corona wires 64 in a corona shield 66. which directs the ions from the corona wire 64 onto the beads 48 on support member 62. The beads are not photoconductive and are therefore unaffected by the electromagnetic radiation produced by corona wires 64.- These beads procede under the force ,of gravity or under mechanical conveyance to cascade over the photoreceptive surface 54 of, for example, a xerographic drum having a grounded conductive substrate 53. The

drum is driven by motor means 56. In this way charge is transferred to the photoconductive layer 54 of the drum.

It should be noted that the optical radiation from the corona wires 64 does not reach the photoconductor 54. Further. it should be noted that by charging a large number of small insu' lating beads 48 it is no longer required that the corona wires 64 produce a uniform emission. Therefore. all of the corona current can be used to charge the beads 48 allowing selective steps taken in the prior art to becliminated, thus, simplifying the corona charging process. The above process produces a great increase in efficiency, since in conventional corona charging of the photoconductor, in order to achieve more uniform charging on the photoconductor, as much as 90 percent of the corona current is directed toward the shield means and thus is wasted. It should also be noted that by employing this technique it is possible to charge uniformly with negative charges since the particles tend to distribute the charge in their cascading action uniformly by their random action whereas in the past uniform charging by negative corona has been a difficult goal due. to pinch effects which produce what are commonly known as hot spots along the coronawire and result in nonuniform charging of the photoconductor when applied directly to the photoconductor. produced by corona wire. I6 around and past electrostatic deflection element 20.

The specific gas selected to be directed by pneumatic pressure from compressed gas bottle 26 While the beads 48 have been referred throughout as small insulating beads, their dimensions andeomposition may vary over a relatively large range. For example, typical bead dimensions may be on the order of 40 to I000 microns. In general,- the smaller the bead size the more uniform the charging. Typi-- cal materials suitable for use as the insulating beads include glass, and polystyrene. v 3

The cascade arrangement may be varied considerably from that shown in FIG.- 4 since it is only necessary to charge the insulating beads 48 in a way which prevents the electromagnetic radiation produced by the'corona from falling directly on the photoconductive mediato be charged and then cascading the small insulating beads 48 over the surface to be charged. The arrangement shown in FIG. 4 is merely illustrative of the one possible embodiment of the present invention and many other variations both for drum and flat plate configurations will be obvious to those skilled in the art. For example, a layer of insulating beads may be deposited on a selenium or similar photoconductive plate to allow induction charging of the photoconductor through the charging of the layer of beads.

Thus, in operation, it is merely necessary to charge a number of small insulating beads by an optically masked corona unit and then bring the beads in contact with the plate or photoconductive material to be charged. The transfer of charge may be madeby contact or induction depending upon the configuration and sequence of steps employed.

Another embodiment is shown in FIG. 5. The operating principle of the embodiment shown in FIG. 5 is essentially the same as that shown in FIG. 4 but in lieu of the small insulating beads 48 an insulating belt is employed. This beltis driven by a driven pulley wheel 76 which is drivenby a motor 78. Belt 80 is then corona charged by corona wire 74 which .is optically shielded from the photoconductive drum comprising photoconductive layer 86' overlying conductor 85.1The drum is driven by motor means 88 The optical shielding of the photoconductor 86 from the light produced by the corona wire 74 may be achieved by the configuration of the insulating belt 80 shown in FIG. 5 and also by shields 72 and if necessary by additional baffles. and stops 70. Once the charge is deposited upon insulating belt 80 by the corona means 74 the insulating belt 80-then passes over pulley rolls 82 and 84 which bring the charges into intimate contact with the photoconductive drum 86 so as to transfer the charge from insulating belt 80 to the photoconductive layer 86.

Again it should be noted that the optical radiation which is deleterious to the efficiency of corona charging is isolated, masked, and prevented from reaching the charged region of the photoconductor. in addition, it isnow possible to use a greater percent of the corona produced to charge the belt than is possible when directly exposing the photoconductor to the corona unit and thereby efficiency is additionally increased. ln the embodiment as shown in H6. 5, it is again merely necessary to charge insulating belt 80 and then bring that insulating belt into contact with the photoconductive media thereby transferring charge to the photoconductive media while at the same time masking and isolating that media from the electromagnetic radiation produced by corona wire 74.

It should be noted that, of course, the present invention is not limited to situations in which a photoconductor is to be charged but the present application is applicable to any situation in which it is desired to produce and utilize corona charging. it is also clear, however. that the problem solved by the present arrangement is most serious in the situations in which sensitive high speed photoconductors are being employed.

Although a specific preferred embodiment of the present invention has been set forth in the detailed description above, the description is not intended to limit the invention to the particular forms or embodiments disclosed herein since they are to be recognized as illustrative rather than restrictive and it will be obvious to those skilled in the art that the invention is not so limited. The invention is declaredto cover all changes and modifications of the specific examples of the invention herein disclosed for purposes of illustration which do not constitute departures from the spirit and scope of the invention.

We claim: I. A method of increasing the efficiency of corona charging comprising: l. applying a potential to a corona charging wire;

2. shielding a photoconductor adjacent said charging wire from the electromagnetic radiation produced by said corona by optical masking;

3. charging an intermediate insulating material with ions produced by said corona charging wire; and

4. bringing said intermediate insulating material into contact with said photoconductor. thereby charging said photoconductor.

2. The method of claim 1 wherein said intermediate insulating material comprises a large number of small insulating beads.

3. The method of claim l wherein said intermediate insulating material comprises an insulating belt.

4. A corona charging device comprising:

l. a corona wire for producing ions when a potential is applied thereto;

2. means for applying a potential to said corona wire;

3. optical mask means for preventing the direct illumination of a photoconductor adjacent said corona wire from electromagnetic radiation produced by said corona wire;

4. means for charging an intermediate insulating material with said ions; and

5. means for bringing said intermediate insulating material into contact with said photoconductor, thereby charging said photoconductor.

5. The apparatus of claim 4 wherein said intermediate insulating material comprises a large number of small insulating beads.

6. The apparatus of claim 4 wherein said intermediate insulating material comprises an insulating belt. 

1. A CORONA WIRE FOR PRODUCING IONS WHEN A POTENTIAL IS APPLIED THERETO;
 2. MEANS FOR APPLYING A POTENTIAL TO SAID CORONA WIRE;
 3. OPTICAL MASK MEANS FOR PREVENTING THE DIRECT ILLUMINATION OF A PHOTOCONDUCTOR ADJACENT SAID CORONA WIRE FROM ELECTROMAGNETIC RADIATION PRODUCED BY SAID CORONA WIRE;
 4. MEANS FOR CHARGING AN INTERMEDIATE INSULATING MATERIAL WITH SAID IONS; AND
 5. MEANS FOR BRINGING SAID INTERMEDIATE INSULATING MATERIAL INTO CONTACT WITH SAID PHOTOCONDUCTOR, THEREBY CHARGING SAID PHOTOCONDUCTOR.
 2. shielding a photoconductor adjacent said charging wire from the electromagnetic radiation produced by said corona by optical masking;
 2. The method of claim l wherein said intermediate insulating material comprises a large number of small insulating beads.
 2. means for applying a potential to said corona wire;
 3. optical mask means for preventing the direct illumination of a photoconductor adjacent said corona wire from electromagnetic radiation produced by said corona wire;
 3. The method of claim l wherein said intermediate insulating material comprises an insulating belt.
 3. charging an intermediate insulating material with ions produced by said corona charging wire; and
 4. bringing said intermediate insulating material into contact with said photoconductor, thereby charging said photoconductor.
 4. A corona charging device comprising:
 4. means for charging an intermediate insulating material with said ions; and
 5. means for bringing said intermediate insulating material into contact with said photoconductor, thereby charging said photoconductor.
 5. The apparatus of claim 4 wherein said intermediate insulating material comprises a large number of small insulating beads.
 6. The apparatus of claim 4 wherein said intermediate insulating material comprises an insulating belt. 